Decumbent or spreading to erect herbs, with cystoliths. Leaves opposite, sessile to petiolate, usually small; blades ovate to lanceolate, with numerous cylindrical cystoliths, membranous, margin entire. Inflorescences of axillary or terminal, densely bracteate dichasiate spikes, spikes solitary or clustered, elongate and cylindric to secund or nearly globose and appearing subcapitate; dichasia opposite, 1-7-flowered, sessile or subsessile, subtended by a bract; bracts opposite, green, ± hyaline, or colored, often spinose-aristate at apex, 1-3-veined; bracteoles 2, 1-veined. Flowers homostylous, subsessile; calyx 5-lobed, lobes heteromorphic, posterior lobe largest, lateral lobes smallest, anterior lobes connate for a greater distance than other lobes (rarely only minutely so or not at all); corolla whitish, yellow, pink, or purplish, often slightly exceeding calyx, tube cylindric or gradually expanded distally into a throat, limb bilipped, upper lip rugulate, emarginate or shallowly 2-lobed, lower lip 3-lobed, corolla lobes imbricate in bud; stamens 4, didynamous, inserted near apex of corolla tube, included in corolla tube or exserted, anthers 2-thecous, thecae subequal to subparallel, equal to unequal inserted, unappendaged or 1 or both thecae minutely appendaged at base, staminodes absent, pollen prolate, 3-colporate, exine reticulate; style exserted from mouth of corolla, stigma appearing entire to 2-lobed. Capsules estipitate, subovoid to subellipsoid, retinacula present, septa with retinacula remaining attached to inner wall of mature capsule; seeds 2-4, homomorphic, lenticular, pubescent with hygroscopic trichomes.
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Herbs [or shrubs], perennial, with cystoliths, often anisophyllous. Leaves opposite; leaf blade margin entire or crenate-serrate. Inflorescences dense spikes or cymes condensed into globose heads, sometimes clustered; bracts and bracteoles present. Calyx 5-lobed; lobes heteromorphic; posterior lobe usually largest; lateral 2 lobes smallest; anterior 2 lobes usually connate to a greater degree than other lobes. Corolla small; tube usually expanded into a distinct throat near middle; limb 2-lipped; lower lip 3-lobed, patent, usually spotted, lobes subequal or middle one slightly larger; upper lip erect or slightly patent, entire to 2-lobed; lobes quincuncial in bud. Stamens 4, didynamous [or with one pair reduced or absent], usually included in corolla tube; filaments short; anthers 2-thecous [or with one pair of anthers sometimes 1-thecous]; thecae oblong, parallel or one lower and somewhat divergent, base muticous or spurred. Ovary with 2 ovules per locule; stigma subcapitate, entire or slightly 2-cleft. Capsule subellipsoid to oblong to linear-conical, lacking a stalk, to 4-seeded; retinacula present. Seeds discoid, pubescent with hygroscopic trichomes.
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